There are several packaging processes known in the literature and recently applied in industry, particularly in the food industry, that involve the deep-drawing of an oriented heat-shrinkable film to form a flexible container. In these methods the product to be packaged is loaded in the container thus obtained, and the package is then closed, once air is evacuated from the inside, with a lid, which may be e.g., a flat film, another deep-drawn flexible container, or a stretched film, that is sealed to the flange of the loaded container. Shrinkage of the packaging material, induced by a heat-treatment, then provides the desired tight appearance to the end vacuum package.
Examples of these methods are for instance those described in DE-A-2,364,565, in US 2005/0173289, or in EP-A-1,557,372.
These methods vary in certain respects, such as the use of a lid which may or may not be heat-shrinkable, may or may not be deep-drawn or may or may not be stretched over the product, and in the manner the package is shrunk, e.g., heating only the deep-drawn container or the whole package, carrying out the heat-shrinking step on the end package exiting the vacuum chamber, or carrying out the heat-shrinking step while the package is still in the vacuum chamber, before or after it is sealed.
These new methods essentially differ from the conventional deep-drawing packaging methods, in the use of a heat-shrinkable flexible film, typically with a thickness in the range of from 40 to 160 μm, instead of a conventional, thicker, non heat-shrinkable laminate. The advantages offered thus mainly reside in the highly reduced amount of packaging material employed and in the improved pack appearance that makes the product more appealing.
The first step, which is common to all the above processes, involves deep-drawing an oriented heat-shrinkable film to form a flexible container, e.g., a sort of a pouch or pocket of the size and dimensions desired and set by the specific mould employed.
Said step which is the key step in all these processes is also the most problematic one, particularly if a large depth, e.g. 60, 80, 100 or more mm, is desired for the container.
The oriented heat-shrinkable film that is used in said thermoforming step must have many attributes to be fit-for-use in these processes:                i) it must be formable to the desired depths and the definition of the container formed should correspond as much as possible to the shape of the mould;        ii) it must have high mechanical properties so that the end package, where the thickness of the packaging material is reduced by the forming step, still has the necessary abuse resistance;        iii) once thermoformed, the film must show a certain minimum % free shrink in both directions and a certain shrink tension to guarantee that after the shrink step, that is carried out at temperatures that do not negatively affect the packaged product, the package appearance is as tight as desired;        iv) at the same time however it should not give the so-called “shrink back” effect, and the container formed will have to maintain as much as possible the size given by the mould; and        v) it should have good optical properties after deep drawing and shrinkage.        
It has been found that the heat-shrinkable films presently used for shrink packaging applications, such as shrink bags or shrink FFS processes, are not fit-for-use for the new “thermoform-shrink” processes as they do not meet most of the above requirements.
The present invention addresses this problem and is directed to an oriented heat-shrinkable film that has the attributes listed above and can thus be suitably employed i.a., in the new “thermoform-shrink” processes.